1. Field of the Invention
The invention relates to an apparatus for dry etching used in semiconductor device manufacturing steps.
2. Description of the Related Art
Many apparatuses for dry etching have been proposed so far, for instance, in Japanese Unexamined Patent Public Disclosures Nos. 62-128122 published on Jun. 10, 1987, 1-172561 published on Jul. 7, 1989, and 3-126225 published on May 29, 1991. FIG. 1 schematically illustrates a typical one of such apparatuses. The illustrated apparatus for dry etching has an etching chamber 101 highly evacuated by a vacuum pump 102. In the etching chamber 101, a lower electrode 103 is disposed near a bottom surface of the chamber 101, and an upper electrode 104 is disposed above and in parallel with the lower electrode 103. To the lower electrode 103 is connected a high frequency power supply 106 through a matching box 105. To the upper electrode 104 is connected a gas introducing pipe 107. The upper electrode 104 is provided at a lower surface thereof with a plurality of openings 109 through which the gas introduced through the pipe 107 is to be blown out, and is electrically grounded.
A material to be etched, which is a semiconductor wafer W in this case, is placed on the lower electrode 103. An etching process gas is introduced into the chamber 101 through the pipe 107 and sequentially the openings 109 of the upper electrode 104, and concurrently the high frequency power supply 106 provides a high frequency voltage with the lower electrode 103, to thereby generate electric discharge in the etching process gas to form a plasma. Thus, the semiconductor wafer W is etched.
However, a conventional apparatus for dry etching such as aforementioned is often accompanied with a problem that if one or more of etching conditions vary such as an etching, pressure, a high frequency electrical power and a gas flow ratio, the uniformity of etching in the wafer tends to have a trade-off relationship with other etching properties such as a profile and selectivity.
For instance, when aluminum is to be etched with the apparatus explained with reference to FIG. 1, if a pressure is set to be high, an appropriate uniformity could be obtained, but a form would be resulted to be isotropic, whereas if a pressure is set to be low, an anisotropic profile could be obtained, but a uniformity would be deteriorated.
In view of this problem, there has been proposed an apparatus for ensuring an anisotropic etching and also enhancing the uniformity in an etched wafer. As illustrated in FIG. 2, the apparatus includes a stationary ring 108 surrounding the semiconductor wafer W placed on the lower electrode 103. The stationary ring 108 controls the discharge of gas present on the wafer W and products of reaction to thereby ensure an appropriate uniformity in etching.
However, when different kinds of layers are to be etched or when, even if the same layers are to be etched, different etching properties such as a profile and a selectivity are required because different functions are required in a semiconductor device, it is necessary to select a process gas and etching condition in accordance with the requirements. Thus, the use of the ring 108 having a fixed height is accompanied with a problem that the etching properties are not always compatible with the etching uniformity.
To solve this problem, it is necessary to use rings having an appropriate height in dependence on etching conditions or a kind of a layer to be etched. However, to use such different rings decreases the availability of the apparatus.
In addition, when laminated layers in which different kinds of layers are laminated are to be etched, a ring which is appropriate to a specific layer is not always appropriate to other layers for obtaining the desired uniformity, resulting in that an appropriate uniformity for all layers cannot be obtained.